Abstract LB-006: Macrophage-dependent activation of Notch1 signaling regulates breast tumor cell intravasation

Abstract

Abstract The process of intravasation, a key component to the metastatic cascade, remains poorly understood. How the multi-cell type tumor microenvironment facilitates tumor cell intravasation is largely unknown. Intravital imaging of rodent mammary tumors has shown that direct contact between a Mena expressing tumor cell, a perivascular macrophage and an endothelial cell forms a microanatomical structure named TMEM (Tumor Microenvironment of Metastasis) which is the site where intravasation occurs in mammary tumors. Clinical studies have shown that the number of TMEM is correlated with increased risk of developing distant metastasis in breast cancer patients. While TMEM is an excellent prognostic marker for predicting metastasis, the mechanisms of TMEM assembly and function are not well understood. Recently, we showed that heterotypic cell contact between tumor cells and macrophages induces the formation of invadopodia in tumor cells, invasive structures necessary for matrix degradation and required for tumor cell intravasation. In further work we found that Notch1, a known receptor involved in heterotypic cell contact signaling, is involved. In the absence of Notch1 signaling, macrophage-induced invadopodium formation and tumor cell intravasation are abolished. This heterotypic tumor cell - macrophage interaction regulates the expression profile of Mena in the tumor cell. Upon touching, the transcription of Mena shows a rapid kinetic response, with detectable changes in single transcriptome activity within 1 hour. Inhibition of Notch1 in vivo results in decreased intravasation of mammary tumor cells. Our findings indicate that Notch1 signaling regulates heterotypic cell contact mediated invadopodium formation, transendothelial migration and intravasation and reveals a novel Notch1/Mena pathway as a molecular target to prevent TMEM function and therefore metastasis. Citation Format: Jeanine Pignatelli, Jose Javier Bravo-Cordero, Minna Roh-Johnson, Saumil Gandhi, Yarong Wang, Robert Singer, Louis Hodgson, Maja Oktay, John Condeelis. Macrophage-dependent activation of Notch1 signaling regulates breast tumor cell intravasation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-006.